Lactobacillus acidophilus is a Gram-positive, rod-shaped, non-spore forming, homofermentative bacterium that is a normal inhabitant of the gastrointestinal and genitourinary tracts. Since its original isolation by Moro (1900) from infant feces, the “acid loving” organism has been found in the intestinal tract of humans, breast-fed infants, and persons consuming high milk, lactose, or dextrin diets. Historically, L. acidophilus is the Lactobacillus species most often implicated as an intestinal probiotic capable of eliciting beneficial effects on the microflora of the gastrointestinal tract (Klaenhammer and Russell (2000) “Species of the Lactobacillus acidophilus complex” Encyclopedia of Food Microbiology, 2:1151-1157. Robinson et al., eds. (Academic Press, San Diego, Calif.)). L. acidophilus can ferment hexoses, including lactose and more complex oligosaccharides, to produce lactic acid and lower the pH of the environment where the organism is cultured. Acidified environments (e.g., food, vagina, and regions within the gastrointestinal tract) can interfere with the growth of undesirable bacteria, pathogens, and yeasts. The organism is well known for its acid tolerance, survival in cultured dairy products, and viability during passage through the stomach and gastrointestinal tract. Lactobacilli and other commensal bacteria, some of which are considered as probiotic bacteria that “favor life,” have been studied extensively for their effects on human health, particularly in the prevention or treatment of enteric infections, diarrheal disease, prevention of cancer, and stimulation of the immune system. Genetic characterization of other Lactobacillus species (e.g., L. johnsonii and L. rhamnosus) has been described (see e.g., U.S. Pat. No. 6,476,209; U.S. Pat. No. 6,544,772; U.S. Patent Publication Nos. 20020159976, 2003013882 & 20040009490; PCT Publication No. WO 2004/031389; PCT Publication No. 2003/084989; PCT Publication No. WO 2004/020467).
During fermentation, lactic acid bacteria are exposed to toxic byproducts of their growth, such as lactic acid and hydrogen peroxide, antimicrobial agents produced by neighboring microorganisms, and deleterious environmental conditions required for proper fermentation of a raw food item. They must also adapt to harsh conditions found in the stomach during ingestion, and severe temperatures associated with storage or production conditions. These bacteria have evolved complex stress response mechanisms to permit their survival under adverse conditions such as heat or cold shock, acid or alkaline shock, osmotic or oxidative stress, and/or starvation.
Microorganisms that can better withstand stressful environments, such as those present during commercial fermentation and storage, are advantageous. Therefore, isolated nucleic acid sequences encoding such stress-related proteins are desirable for use in engineering microorganisms, including Lactobacillus acidophilus, to have an increased ability to tolerate various stress conditions.